Lightweight heat-insulating building material having frost resistance

ABSTRACT

A lightweight heat-insulating building material which has excellent frost resistance and a low price is provided. The lightweight heat-insulating building material having frost resistance is produced by molding a mixture of raw materials containing glass powder, a foaming agent, a crystallization inhibitor, and a frost inhibitor so as to form a molded body, and firing the molded body so as to foam the molded body.

FIELD OF THE INVENTION

[0001] The present invention relates to a lightweight heat-insulatingbuilding material having frost resistance.

BACKGROUND OF THE INVENTION

[0002] Foamed glass is used as interior materials, exterior materials,and walls of housings and buildings due to its heat insulation and soundabsorbing properties.

[0003] The following Japanese patent publications describe foamed glass.

[0004] (i) JP S61-2618B discloses foamed glass which has bulk density of0.20-0.34 g/cm³ and which is produced by adding 1.5-9.5% by weightdolomite (MgCO₃.CaCO₃) powder as a foaming agent into glass powder ofsoda-lime glass or the like so as to form a mixture, and heating themixture at 700-780° C. at least for one hour.

[0005] (ii) JP H06-99160B discloses laminated foamed glass consisting ofa foamed glass layer having bulk density of 0.3-0.6, a medium-foamedglass layer (bulk density 1.0-1.7), and a non-foamed glass layer. Rawmaterials for the respective layers are successively molded to belaminated integrally and fired under pressure, thereby producing thelaminated foamed glass.

[0006] (iii) JP H11-79866A discloses foamed glass which is produced bycoating foamed glass beads with coating material comprising clay andglass, dry-pressing the coated beads, and firing the dry-pressed body at800-1100° C.

[0007] The foamed glass of the above (i) and the laminated foamed glassof the above (ii) have poor frost resistance because they have highwater absorption. The foamed glass of (i), (ii) has thin cell walls andboundary faces between glass phases and crystal phases, and the thincell walls and the boundary faces can be dissolved by water so as toform pores through which the water can easily enter into the glass. Thefoamed glass of (i), (ii) has small pores which are already formed inglass at cell walls during firing. In the early stage of waterabsorption, the glass seems to have low water absorption in appearancedue to insufficient replacement between gas or air in the cells andwater. However, the glass absorbs a large amount of water finally tohave high water absorption. Although the foamed glass has relatively lowwater absorption of 5-15% by weight in the normal condition, the foamedglass has significantly high water absorption of 50-100% by weight whenboiled or soaked for a long period of time. Therefore, the foamed glassis easy to be damaged or broken due to repetitions of freezing andthawing of absorbed water.

[0008] The foamed glass of the above (iii) is produced with a largeamount of the coating material which is 30-80 wt. % relative to thefoamed glass beads. The foamed glass of (iii) is produced through manysteps including of producing the foamed glass beads, molding them, andfiring them at a high temperature of 800-1100° C., so that the foamedglass has a high manufacturing cost.

OBJECT AND SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to provide a lightweightheat-insulating building material having frost resistance which hasexcellent frost resistance and can be manufactured at low cost.

[0010] The building material of the present invention is produced bymolding a mixture of raw materials containing glass powder, a foamingagent, a crystallization inhibitor, and a frost inhibitor so as to forma molded body, and firing the molded body so as to foam the molded body.

[0011] The building material of the present invention has excellentfrost resistance, lightweight, and heat insulation property.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The lightweight heat-insulating building material having frostresistance according to the present invention is produced by mixing rawmaterials including glass powder, a foaming agent, a crystallizationinhibitor, and a frost inhibitor, molding the mixture, and firing themolded body to foam the molded body.

[0013] Raw material for the glass powder may be soda-lime glass used forglass plates and glass bottles. Examples of the raw material includeglass cullet obtained by grinding waste glass such as scraps of glassplates or glass bottles from plants for manufacturing glass plates andplants for processing glass, and construction and demolition wasteglass.

[0014] The foaming agent can be at least one selected from the groupconsisting of carbonate and aluminium metal. The carbonate includesdolomite and calcium carbonate. The calcium carbonate may be limestone.

[0015] When the foaming agent is composed of carbonate only, the mixtureof raw materials contains carbonate preferably in an amount of 0.3 to10% by weight, more preferably 0.5 to 6% by weight.

[0016] When the foaming agent is composed of aluminium metal only, themixture of raw materials contains aluminium metal preferably in anamount of 0.1 to 5% by weight, more preferably 0.3 to 1.5% by weight.

[0017] When the foaming agent is composed of carbonate and aluminiummetal, the mixture of raw materials contains carbonate preferably in anamount of 0.5 to 5% by weight and aluminium metal preferably in anamount of 0.3 to 1.0% by weight. Carbonate and aluminium metal arepresent in the mixture preferably in an amount of 1.0 to 5% by weight intotal, more preferably 2 to 4% by weight in total.

[0018] If the proportion of carbonate exceeds the aforementioned range,calcium oxide (CaO) and/or magnesium oxide (MgO) as decompositionproducts of the carbonate may crystallize the glass so as to increasethe softening point of the glass. The increase in the softening pointsuppresses the glass to foam whereby decreasing the bulk density ofobtained foamed glass. If the proportion of carbonate is lower than theaforementioned range, the amount of carbonic acid gas generated from thecarbonate should be insufficient to foam the glass whereby decreasingthe bulk density of obtained foamed glass. If the proportion ofaluminium metal exceeds the aforementioned range, the foamed glass hascontinuous cells due to excessive foaming so as to unduly increase thewater absorption, leading to poor frost resistance. On the other hand,if the proportion of aluminium metal is lower than the aforementionedrange, the glass foams insufficiently so as to reduce the bubble ratioand the bulk density of the foamed glass.

[0019] When the foaming agent is composed of aluminium metal only, thefoamed glass appears to be black colored that may sometimes spoil theappearance of the foamed glass. When the foaming agent is composed ofaluminium metal and carbonate, the foamed glass appears to be lightcolor that may be good in appearance.

[0020] The crystallization inhibitor can be at least one selected fromthe group consisting of water glass, sodium silicate, boric acid, borax,and Glauber's salt. The mixture of raw materials contains thecrystallization inhibitor preferably in an amount of 1 to 10% by weight,more preferably 3 to 7% by weight expressed as sodium silicate. Thecrystallization inhibitor lower than this range of proportion allowsglass to be easily crystallized, thus suppressing the glass to foam. Thecrystallization inhibitor exceeding this range of proportion undulylowers the softening point of glass so as to allow the glass to foamexcessively, whereby the foamed glass has poor strength and poor frostresistance.

[0021] The frost inhibitor is preferably material of calcium silicateseries and may be at least one selected from the group consisting oflightweight aerated concrete, mortar, concrete, cement, calcium silicateplate, asbestos cement plate, wollastonite, and asbestos. The frostinhibitor may be construction and demolition waste of calcium silicateseries.

[0022] The mixture of raw materials contains the frost inhibitorpreferably in an amount of 0.5 to 30% by weight, more preferably 3 to12% by weight.

[0023] The frost inhibitor lower than this range of proportioninsufficiently prevents the frost damage. The frost inhibitor exceedingthis range of proportion allows the glass to be crystallized so as to ;increase the softening point of the glass, thus suppressing the glass tofoam. Foamed glass containing excess amount of frost inhibitor sufferseasily frost damage because water is absorbed via the frost inhibitor.

[0024] The mixture of raw materials may contain dirt such as soil, wood,paper, plastic, and metal earned from the construction and demolitionwaste in an amount of 10% or less by weight.

[0025] The foamed glass as the lightweight heat-insulating buildingmaterial having frost resistance according to the present invention ismanufactured as follows.

[0026] First, the glass cullet, the foaming agent, and thecrystallization inhibiter are milled and mixed by a mill to produce apowder mixture A. The mill may be a ball mill or a vibrating mill. Aftermilled, the powder mixture A for the lightweight heat-insulatingbuilding material having frost resistance preferably has grain sizes of87 μm or less, more preferably 43 μm or less and, in addition, it isdesirable that the powder of which grain size is 10 μm or less accountsfor 30 percent or more. The powder mixture A having such grain sizes iseasy to disperse. A foamed glass produced by using this powder mixturehas closed cells and thus has low water absorption. The powder mixtureof which grain size exceeds the aforementioned range easily makescontinuous cells in the foamed glass.

[0027] Separately from the aforementioned milling process, the frostinhibitor is milled to be powder. The powdered frost inhibitor and thepowder mixture A are mixed. The powdered frost inhibitor may have grainsize slightly coarser than the powder of the mixture A. The powder ofthe powdered frost inhibitor preferably includes particles having grainsize from 10 to 43 μm in an amount of 50 percent or more.

[0028] The reason of milling the frost inhibitor separately from theglass cullet, the foaming agent, and the crystallization inhibitor isthat the frost inhibitor is milled to be coarser than the powder mixtureA. Foamed glass produced by using frost inhibitor having too fineparticles includes crystals of wollastonite (CaO.SiO₂) created byreaction with the frost inhibitor, and the wollastonite inhibits theglass to foam. In addition, a SiO₂ deficient glass phase having low SiO₂concentration can be created around the crystal of wollastonite. ThisSiO₂ deficient glass phase is easily dissolved by water so as to formpores therein, thus increasing the water absorption of the foamed glass.

[0029] The powder mixture A including the glass cullet, the foamingagent and the crystallization inhibitor is mixed with the powdered frostinhibitor so as to prepare a powder raw material. The powder rawmaterial may be press-molded by a mold.

[0030] To prevent a molded body from cracking when it is carried orfired, water and/or water glass may be added to the powder raw materialto pelletize and the pellets may be loaded in the mold to form a moldedbody. It is preferable that more than 70% of the pellets have a diameterfrom 0.3 to 2 mm. The pellets having such diameter can be tightly loadedin the mold so as to form a molded body having high bulk density. Afoamed glass produced by firing the molded body having high bulk densityhas low bulk density and low water absorption.

[0031] Use of pellets having diameter exceeding the aforementioned rangeproduces a large volume of air gaps in the molded body. The air gapsproduce continuous pores in the foamed glass after fired, andundesirably increases the water absorption of the foamed glass.

[0032] After loading the raw material composed of the powder and/or thepellets into the mold, the raw material in the mold may be pressed so asto provide high bulk density to the molded body. This high bulk densityprovides to low bulk density and low water absorption to the foamedglass as mentioned above.

[0033] In an embodiment of the present invention, the raw material ismolded by a mold placed on a mesh belt. The molded body is released fromthe mold inside or outside a kiln. A parting agent may be previouslyapplied to the mesh belt. The parting agent may be pulverized alumina,clay, bentonite, or mica.

[0034] The molded body is preferably fired at 700-800° C., morepreferably at 710-770° C. The kiln may be a mesh belt kiln. The firingtime is preferably from 10 to 60 minutes, more preferably from 15 to 30minutes. Firing temperature or time lower and shorter than theaforementioned range makes the glass to foam insufficiently, so that thefoamed glass has high bulk density. On the other hand, firingtemperature or time exceeding the aforementioned range makes the glassfoaming excessively, so that the foamed glass has continuous cellswhereby increasing the water absorption thereof.

[0035] A foamed glass produced in this manner has preferably bulkdensity from 0.2 to 0.8.

[0036] The lightweight heat-insulating building material having frostresistance of the present invention may be composed of theaforementioned foamed glass only or may be composed of the foamed glassand compact non-foamed glass. For example, the building material maycomprises the foamed glass layer and a compact glass layer laminated onat least a portion of surfaces of the foamed glass. The compact glasslayer improves the appearance and water-proof property of the buildingmaterial. The building material according to the present invention maybe a laminated body comprising a foamed glass layer and another foamedglass layer which is made of waste glass including dust and is laminatedon the foamed glass layer. A compact glass layer may be further formedon at least a portion of surfaces of the laminated body.

[0037] Function mechanism of exhibiting the excellent frost resistancein the foamed glass according to the present invention will beconsidered in detail as follows.

[0038] Conventional foamed glass having closed cells actually absorbswater little by little for a long period of time. As a result, thefoamed glass is cracked due to the frost damage. This is becauseportions having thin cell walls (walls of cells formed in the foamedglass) and/or boundary faces between a glass phase and crystal phase maybe dissolved by water so as to form pores through which water can easilyenter into the glass. Although the conventional glass has low waterabsorption at an early stage of absorbing water due to insufficientreplacement between gas or air in the cells and water, the conventionalfoamed glass have small pores which are already formed at cells duringfiring so that water is absorbed therethrough.

[0039] On the other hand, the foamed glass as building materialaccording to the present invention has not only low ordinary waterabsorption, but also low boiled water absorption and low long-term waterabsorption because it contains the frost inhibitor. The frost inhibitoralso increases the strength of the lightweight heat-insulating buildingmaterial.

[0040] According to the present invention, the mixing ratios of thecrystallization inhibitor and the frost inhibitor can be controlled insuch a range allowing foaming at a low temperature. The foamed glass asbuilding material of the present invention is fired at a temperaturelower than the conventional foamed glass. The foamed glass of thepresent invention can be manufactured at a low cost without any specialsystem in the mold or the kiln. The building material of the presentinvention can be made without necessity of foaming and firing forpreviously producing foamed beads. The building material of the presentinvention can be manufactured with a reduced number of steps and at lowcost.

[0041] Hereinafter, examples and comparative examples will be described.

[0042] Raw materials used in the examples and the comparative examplesare as follows:

[0043] <Glass>

[0044] FL: waste glass of float plate glass

[0045] BN: waste glass of glass bottles

[0046] <Foaming Agent>

[0047] D: dolomite

[0048] A: aluminium metal

[0049] <Crystallization Inhibitor>

[0050] N: sodium silicate powder (No. 3) Na₂O.3SiO₂

[0051] W: water glass (No. 3)

[0052] B: absolute borax Na₂B₄O₇

[0053] <Frost inhibitor>

[0054] L: ALC powder

[0055] M: mortar board powder

[0056] K: calcium silicate board powder

[0057] S: asbestos powder

EXAMPLES 1-25, COMPARATIVE EXAMPLES 1-5

[0058] Respective foamed glass was manufactured with proportions ofcomponents of raw materials as shown in Table 1.

[0059] The glass, the foaming agent, and the crystallization inhibitorwere milled and mixed in such a manner as to have powder of which 30percent or more has grain size from 1 to 10 μm, and then added and mixedwith the frost inhibitor which was previously milled in such a manner asto have powder of which 50 percent or more has grain size from 10 to 43μm. 23% by weight water was added into the mixture and then pelletizedby a pan-shaped pelletizer in such a manner as to have pellets of which70 percent or more have diameter from 0.3 to 2 mm. In case of usingwater glass, the water glass was not added during milling and mixingstep and was added instead of water during pelletizing step, as the nextstep of the milling and mixing step, so as to make pellets in the samemanner. After the pelletizing step, the pellets were aged in the sealedstate for 18 hours and then dried at 50° C. for 24 hours.

[0060] Obtained material pellets were then formed and fired as follows.

[0061] First, the material pellets were loaded on a shelf of 8 mm inthickness which is made of mullite cordierite and surrounded by a mold.A mesh belt of 1100×1400 mm was previously disposed on the shelf as abase sheet. The mesh belt was prepared by applying and drying slurry ofpulverized alumina and mica.

[0062] The loaded material pellets were pressed from the above atpressure about 0.2 kg/cm² to eliminate irregularities nor gaps therein.After the pressing, the mold was released.

[0063] The pressed body was fired with a large-size electric furnace(kanthal furnace) by raising the temperature at a raising rate 7.5°C./min. and retaining the pressed body at the maximum temperature 750°C. (730° C. in case having the frost inhibitor mixed) for 30 minutes.After that, the temperature was cooled at a rate 1° C./min. The maximumtemperature was selected to obtain most suitable bulk density and waterabsorption for every proportions of components based on pilot studies.

[0064] The bulk density of the fired body after firing was measured andthe result is shown in Table 1. Comparative Examples 1, 3 containing nocrystallization inhibitor nor frost inhibitor and Comparative Example 4containing no frost inhibitor had low bulk density and were thereforeconsidered as good foamed glass in appearance. On the other hand,Comparative Examples 2, 5 containing the frost inhibitor but nocrystallization inhibitor were little foamed and were still in the firedstate.

[0065] Then, obtained fired bodies were cut and grinded both surfacesthereof to get specimens for evaluation. The flexural strength, theordinary water absorption, the boiled water absorption, and the freezingand thawing endurance (frost resistance) were measured in the followingmethods for every specimens and the results are shown in Table 1.

[0066] <Flexural Strength>

[0067] The measurement was conducted at a loading speed (cross headspeed) 2 mm/min. by using an Auto Graph manufactured by Simadzu Corp.

[0068] <Ordinary Water Absorption>

[0069] Variations in weight of each specimen was measured after limmersed at water depth 300 mm for 48 hours.

[0070] <Boiled Water Absorption>

[0071] Each specimen was immersed in cold water and the water wasboiled. The specimen was immersed for 3 hours after boiled and was thencooled for one night. At this point, variations in weight of thespecimen was measured.

[0072] <Freezing and Thawing Endurance>

[0073] The measurement was conducted by using a frost resistance testermanufactured by Marui Corporation in accordance with JIS A 5422. Themeasurement conditions are as follows: the dimension of specimens is100×200 mm; and one frost-defrost cycle for 3 hours comprises freezingin air at −20° C. and thawing in water at +20° C. The specimens weresometimes observed to record the number of cycles at which each specimenis broken. The cycle was stopped at the 600th cycle. Examples brokenafter 300 cycles were evaluated as “very god” examples broken after 250cycles before 300 cycles were evaluated as “good”, and examples brokenbefore 250 cycles were evaluated as “bad”. TABLE 1 Composition of RawMaterials (Balance = Glass) Crystallization Ordinary Foaming AgentInhibitor Frost Inhibitor Firing Bulk Flexural Water Boiled WaterFreezing/Thawing Kind of Mixing Ratio Mixing Ratio Mixing RatioTemperature Density Strength Absorption Absorption Endurance Glass Kind(% by weight) Kind (% by weight) Kind (% by weight) (° C.) (g/cm³) (MPa)(% by weight) (% by weight) Cycle Evaluation Comparative 1 FL D 2 — 0 —0 730 0.28 2.0 11 159 72 bad Example 2 FL D 2 — 0 L 3 750 0.83 7.5 5 9296 bad Example 1 FL D 2 N 5 L 3 750 0.37 3.7 8 30 600 very good 2 FL D 2N 5 L 7 750 0.42 4.2 12 33 600 very good 3 FL D 2 N 5 M 5 750 0.41 4.0 632 600 very good 4 FL D 2 N 5 M 10 750 0.49 5.0 11 44 600 very good 5 FLD 2 N 5 K 5 750 0.35 3.4 13 52 600 very good 6 FL D 2 N 5 K 10 750 0.403.7 10 48 600 very good 7 FL D 2 N 5 S 3 750 0.39 4.0 7 29 600 very good8 FL D 2 N 5 S 7 750 0.45 4.5 5 38 600 very good 9 FL D 2 W 10 L 7 7500.39 3.8 14 43 600 very good 10 FL D 2 B 3 L 7 750 0.45 3.8 9 40 396very good 11 BN D 2 N 5 L 7 750 0.40 3.5 11 40 600 very good 12 FL D 2 N5 S 3 750 0.36 3.3 9 45 600 very good Comparative 3 FL D 4 — 0 — 0 7300.25 1.7 15 218 24 bad Example 4 FL D 4 W 10 — 0 730 0.21 1.5 7 58 72bad 5 FL D 4 — 0 L 3 750 0.70 7.0 6 81 120 bad Example 13 FL D 4 N 5 L 3750 0.32 3.1 7 30 600 very good 14 FL D 4 N 5 L 7 750 0.38 3.8 9 24 600very good 15 FL D 4 N 5 M 5 750 0.36 3.5 7 36 600 very good 16 FL D 4 N5 M 10 750 0.41 4.1 11 39 600 very good 17 FL D 4 N 5 K 5 750 0.30 2.914 33 600 very good 18 FL D 4 N 5 K 10 750 0.35 3.4 10 38 600 very good19 FL D 4 N 5 S 3 750 0.33 3.2 8 29 600 very good 20 FL D 4 N 5 S 7 7500.40 3.9 7 37 600 very good 21 FL D 4 W 10 L 7 750 0.36 3.2 7 47 600very good 22 FL D 4 B 3 L 7 750 0.42 3.4 15 48 258 good 23 BN D 4 N 5 L7 750 0.37 3.3 13 42 600 very good 24 BN D 4 N 5 S 3 750 0.33 3.0 10 46600 very good 25 FL A 0.5 N 5 L 7 750 0.46 3.9 8 37 600 very good

[0074] Products of the present invention containing both thecrystallization inhibitor and the frost inhibitor as additives areslightly inferior in bulk density to products without containing theseadditives, but are excellent in flexural strength as compared to theproportional equation of density-flexural strength of the productswithout containing these additives.

[0075] There is no significant difference in the ordinary waterabsorption among the products, although there is significant differencesin the boiled water absorption among them. That is, the products withoutcrystallization inhibitor and frost inhibitor have 100% or more ofboiled water absorption while the products of the present invention have50% or less of boiled water absorption and therefore have excellentfreezing and thawing endurance.

What is claimed is:
 1. A lightweight heat-insulating building materialhaving frost resistance comprising foamed glass, said foamed glass beingproduced by molding a mixture of raw materials containing glass powder,a foaming agent, a crystallization inhibitor, and a frost inhibitor soas to form a molded body, and firing the molded body so as to foam themolded body.
 2. A lightweight heat-insulating building material havingfrost resistance according to claim 1, wherein said crystallizationinhibitor comprises at least one selected from the group consisting ofwater glass, sodium silicate, boric acid, borax, and Glauber's salt. 3.A lightweight heat-insulating building material having frost resistanceaccording to claim 1 or 2, wherein said frost inhibitor is a material ofcalcium silicate series.
 4. A lightweight heat-insulating buildingmaterial having frost resistance according to claim 1 or 2, wherein saidfrost inhibitor is construction and demolition waste of calcium silicateseries.
 5. A lightweight heat-insulating building material having frostresistance according to claim 3 or 4, wherein said frost inhibitor is atleast one selected from the group consisting of lightweight aeratedconcrete, mortar, concrete, cement, calcium silicate plate, asbestoscement plate, wollastonite, and asbestos.
 6. A lightweightheat-insulating building material having frost resistance according toany one of claims 1 through 5, wherein said foaming agent is at leastone selected from the group consisting of carbonate and aluminium metal.7. A lightweight heat-insulating building material having frostresistance according to any one of claims 1 through 6, wherein themixture of raw materials contains the crystallization inhibitor in anamount of 1 to 10% by weight expressed as sodium silicate.
 8. Alightweight heat-insulating building material having frost resistanceaccording to any one of claims 1 through 7, wherein the mixture of rawmaterials contains the frost inhibitor in an amount of 0.5 to 30% byweight.
 9. A lightweight heat-insulating building material having frostresistance according to any one of claims 1 through 8, wherein themixture of raw materials contains, as the foaming agent, one of 0.3 to10% by weight carbonate and 0.1 to 5% by weight aluminium metal.
 10. Alightweight heat-insulating building material having frost resistanceaccording to any one of claims 1 through 8, wherein the mixture of rawmaterials contains, as the foaming agent, 0.5 to 5% by weight carbonateand 0.3 to 1% by weight aluminium metal.
 11. A lightweightheat-insulating building material having frost resistance according toclaim 10, wherein the total of the carbonate and the aluminium metal is1 to 5% by weight.
 12. A lightweight heat-insulating building materialhaving frost resistance according to any one of claims 6 through 11,wherein the carbonate is at least one of dolomite and calcium carbonate.13. A lightweight heat-insulating building material having frostresistance according to any one of claims 6 through 11, wherein thecarbonate is dolomite.
 14. A lightweight heat-insulating buildingmaterial having frost resistance according to any one of claims 1through 13, wherein the molded body is fired at a temperature from 700to 800° C.